A new study on intermittent fasting

Mates, I have written about intermittent fasting previously (CLICK HERE) and one of the things I noticed when researching the post was the dearth of research on time restricted feeding style fasting protocols. Therefore, it was very interesting to see a piece of research come out this month comparing a time restricted feeding style intermittent fasting protocol to a normal diet.

In this post I want to discuss the findings and hopefully explain what they all mean. Feel free to add your opinions to the mix in the comments below!

The experimental set up:

34 males with a good history of resistance training (~5 years) were split into two groups of 17. Group one was the ‘time restricted feeding’ (TRF) group and group two was the ‘normal diet’ (ND), or control group. Both groups had their diets analysed via a 7-day food diary prior to the study starting. For the 8-week study period, both groups continued to eat ‘maintenance calories’ with the only difference being the timings of their meals.

Group one (TRF) ate meals at 12pm, 4pm and 8pm with a 20g whey protein shake 30 minutes after training

Group two (ND) ate meals at 8am, 1pm and 8pm with a 2g whey protein shake 30 minutes after training.

Both groups ate approx. 3000 kcals per day with a 50,25,25 split of carbohydrate, fat and protein. During the study period, both groups trained three times per week, with the following routine:

All exercises were performed for 3 sets of 6-8 reps with a load of 85-90% of their one rep max. 3 minutes of rest were given between each set. Training sessions were performed between 4 and 6 pm on workout days.

All make sense so far?

Here is what happened…

A number of measurements were taken, all of which are described in the paper linked above. Here are the variables that showed a significant change over the eight weeks.

Fat mass decreased – on average the TRF group lost 1.6 kg of fat mass

Adiponectin increased – a hormone that is involved in the regulation of metabolism, amongst other things

IL-6, TNF- α and IL-1 β decreased – all three are markers of inflammation

Testosterone and IGF-1 decreased – both anabolic hormones. However, this decrease did not correspond to unfavourable reductions in body composition or strength measures

Blood glucose and insulin decreased – could possibly be related to the increased adiponectin levels, and an improved insulin sensitivity

Put together, this all means that the subjects in the fasting group lost fat mass, but held onto fat free mass (despite a reduction in anabolic hormones), shifted towards burning more fat at rest, increased insulin sensitivity, reduced inflammatory markers and improved their blood lipid profile. All pretty good things! However, there are a couple of things to consider when taking all this in…

Both groups started with a resting energy expenditure of approx. 1900 kcals/day (1880 and 1900). Not much in it. But, according to the food diary collection, the fasting group ate an average of 2735 kcals per day and the control group ate 2910 kcals per day – a 175 kcals difference. Over 8 weeks this would equal 9800 kcals, which would equate to about 1.1 kg of fat (9 kcals per 1 gram of fat). Whether the subjects ate less as a result of fasting, or there is an inaccuracy within the food diaries isn’t known (food diaries can be inaccurate, but are sometimes the only/best option for these kind of studies)

The fasting group’s meals were closer to their workout – meals at 12pm, 4pm and 8pm with training between 4-6pm meant that training was sandwiched by two meals. Compare this to the control group who ate at 8am, 1pm and 8pm. The results seen may be purely down to the meal timing relative to exercise rather than the actual fasting.

At only 8 weeks, the effects cannot be extrapolated out into the long term. A longer study may have shown the decrease in anabolic hormones to eventually have a deleterious effect on body composition and performance variables – we simply don’t know.

All I all, I hope you agree that it is an interesting study and hopefully one of many more to come investigating IF, a dietary strategy that appeals to me due to its ease of set up and practicality. Remember though, no matter what amazing outcomes a dietary protocol promises, the level of success you see will always boil down to the basic principles (energy balance, sustainability and progression).

Here is an infographic I made to show the key information from the study: